1. Field of the Invention
The present invention is directed to a respirator of the type having an inspiration gas flow which is controlled by the expiration gas flow.
2. Description of the Prior Art
A respirator of the type described above is described in the Training Manual for the Servo Ventilator 900 C, manufactured by Siemens. Various respiration modes can be set using this ventilator. One of these modes is spontaneous respiration with continuous positive aspiration airway pressure (CPAP). CPAP is particularly used in neonatal respiratory care. Initiation of the inspiration phase in this mode is triggered by the patient when, for example given an inhalation attempt by the patient, the pressure in the expiration line falls below an adjustable level. The inspiration valve then opens and breathing ensues without further assistance by the ventilator, i.e., the patient controls, among other things, the breathing rate and the tidal volume. The inspiration is ended, and expiration is initiated, in a similar manner dependent on certain parameters. During the entire time, the expiration valve regulates the expiration pressure to a set PEEP (positive end-expiratory pressure) value, so that a continuous, positive respiratory path pressure is maintained.
Instead of pressure-dependent triggering, it is also known to trigger the ventilator given defined changes in the gas flow.
When providing respiratory therapy to infants and, in particular, premature babies, such triggering may be difficult under certain circumstances. Given pressure-controlled triggering, the infant must first produce a certain under-pressure before the ventilator starts a new inspiration phase. This necessary exertion can complicate the treatment of such infants. Additionally, disturbing delays can arise when switching a respirator of the type described above from the expiration phase to inspiration phase, because the gas column which is present in the gas lines between patient and the ventilator has a certain inertia, which must be overcome. An undesired time thus passes until fresh respiratory gas proceeds from the inspiration line to the airways and lungs of the patient when switching from the expiration phase to the inspiration phase.